The present invention relates to a device for cutting band-shaped or cord-shaped material, in particular for manufacturing staple fibers, having a cutting device in the form of a cutter roller, with the cutter blades, which point outward with their cutting edges, representing a winding body which carries the material to be cut in radially superimposed coil layers, and the coil layer located radially innermost in each case is pressed against the cutting edges by an externally acting pressure and cut.
Such a device is known from U.S. Pat. No. 3,503,100. It consists of two circular disc-shaped cutter holders, of which the upper one is made as a disc and the lower one is made as a ring and which are held at a distance by radially outward-pointing cutter blades which are arranged at regular spacings over the entire periphery. These cutter holders, together with the cutter blades, form the winding body, onto which the material to be cut is firmly wound, with the layer which is located innermost in each case being cut into portions, the length of which is determined by the distance of the cutter blades from one another. If necessary, the pressure on the coil layers is intensified by an externally acting pressure device.
The cut fibers are pressed through the intermediate spaces between the cutter blades into the inside of the cutting device, from where they fall outward by the force of gravity or possibly even by suction action through that opening which is enclosed by the lower, annular cutter holder.
In this known device, the cutters provided as cutting edges can represent the only connection between the two cutter holders. For stability reasons, however, it is preferred that the two cutter holders are connected to one another by a plurality of U-shaped connecting pieces which extend parallel to one another at a distance and are connected to the two cutter holders by brazing or a similar method of fastening. These U-shaped bodies have a narrow slot which is continued in the upper cutter holder and which serves to accommodate the cutter blades.
This known device has the disadvantage that bending stress of the cutter blades occurs in operation, which bending stress leads to deformation and frequently to fractures of the cutter blades. Such fractures must be rectified immediately, because the cutting device is incapable of operating in the event of such a single fracture.
The consequence of this is that usually only relatively thick cutter blades can be used in such devices, which in turn means that the staple length of the fibers has a lower limit, and in fact to 4 to 8 times the blade thickness.
Attempts have therefore already been made repeatedly to counteract the frequent cutter fractures in another way. Thus it has been proposed according to the DE No. 2,609,386 to combine at least two of such winding body-like cutting devices with one another coaxially, with it being possible for the cutter spacings of the combined units to be equal inter alia. The strand to be cut can therefore be distributed over both cutter rollers and thus the pressure on the cutter blades can be reduced.
However, considerably more complicated and expensive apparatus has to be accepted for this increase in production reliability, because layers for two, superimposed rows of cutter blades have to be provided in the central, annular cutter holder. Moreover, this design leads to a reduction in the height of the openings between the cutter blades, which height, if a fiber blockage is to be avoided, places limits on the cutting speed.
According to U.S. Pat. No. 4,528,877 a simpler solution to the problem with respect to the apparatus is proposed inasmuch as only three regularly spaced cutter mountings are provided which carry only one set of cutter blades; that is, the central cutter holder is penetrated by the cutter blades and is only used to reduce the bending stress of the cutter blades. Here, too, compared with cutter rollers without this center strengthening, a considerable reduction in the inside diameter of the openings through which the staple fibers are to be pushed has to be accepted. In the two known solutions, moreover, the division of the original strand is difficult, because the threads do not lie exactly parallel and cling to the tow-separating members.